Biomarkers for Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis: Possible mechanisms mediating neurodegeneration

Abstract

Since the mid-1800s, Multiple Sclerosis (MS) has been considered an episodic-inflammatory disorder of the central nervous system (CNS) characterized by inflammatory plaques with demyelination and relative preservation of axons. MS is believed to be an autoimmune disorder driven by encephalitogenic T cells which can attack the myelin sheath after activation in the periphery of the immune system. However, recent studies have rediscovered neurodegenerative components of the disease like axonal loss, and neuronal atrophy which seem to be the histopathological correlates of progressive clinical disability in MS patients. For this reason the focus in MS research increasingly includes the study of neurobiological aspects in addition to the classical neuroimmunological features. Despite the profound understanding of the different aspects of the pathogenesis of MS there is still a major inadequacy of effective long-term therapeutic interventions and early diagnostic measures. Moreover, the vast majority of therapeutic agents used in clinical trials today are directed against the immunological features of the disease, leaving for the most part untreated the disease processes that lead to irreversible CNS dysfunction in the patients. Therefore developing new therapies for MS that are aimed at preventing or repairing one or more of these disease mechanisms is of great importance. The shortcoming of effective long term treatment can be partially ascribed to the oversimplification of MS as an inflammatory, demyelinating disease and employment of conventional concept driven approaches, which deal with a limited number of molecular components at a time. Therefore more recently MS research aims to get a better understanding of the molecular mechanisms that contribute to the clinical disability as well as the discovery of biomarkers that specifically mediate certain disease processes. This approach calls for the use of unbiased methods that allow large scale monitoring of gene and gene product alterations. It is hoped that this strategy will lead to an improved understanding of critically involved disease pathways rather than just components thereof. The advent of global screening technologies in genomics and proteomics offers the opportunity to accelerate the search of new pathological pathways and identify new therapeutic targets and biomarkers in an unbiased manner. Studies that have conducted large scale transcriptional profiling of lesions from the brains of patients with MS have led to several new targets and pathways for potential interventions. However, the interrogation of only gene-based expression patterns is insufficient for the dissection of a disease phenotype. Moreover, the functional properties of many proteins are regulated by post-translational modifications (PTM) and alternative splicing, which cannot be detected by transcript analysis. As proteins are the functional molecules that reflect the dynamic physiological status of tissues and cells we have begun to analyze global changes in protein expression and modification in MS and a relevant animal model of the disease, Experimental Autoimmune Encephalomyelitis (EAE), that is commonly used. In this study we conducted for the first time protein expression and protein phosporylation state analysis, of brain and spinal cord tissues from different models and stages of EAE. These included proteolipid protein (PLP) and myelin oligodendrocyte glycoprotein (MOG) induced passive and active EAE in early, middle and full blown disease stages. Tissue level analysis as the first step in proteome analysis gives access to the primary mediators of a given physiological state. We observed a number of EAE specific protein expression and post-translational modification differences. These include protein phosphorylation states that are conserved between the different Experimental Autoimmune Encephalomyelitis models. Variations between early and late disease stages of Experimental Autoimmune Encephalomyelitis were also detected. Proteome analysis was also extended to MS specimens in order to validate the EAE findings in MS. The ultimate goal is to discover protein regulation or modification characteristics that are unique to EAE and /or MS, and provide insights into the molecular mechanisms and pathways that contribute to the deleterious clinical outcome of MS. For this purpose the functional and biological roles of the protein markers were interrogated by extensive database and literature mining. Functional classification of the proteins that we have identified reveals their association with different molecular disease processes. The results are a reflection of the neurodegenerative process in EAE that can lead directly or indirectly to neuronal and axonal damage. Disease process-specific protein markers are targets for therapeutic interventions for specific and restricted blocking or enhancement of gene-products in order to impede disease processes.

Multiple Sklerose ist eine degenerative Erkrankung des zentralen Nervensystems. Hauptmerkmal dieser Erkrankung ist eine fortschreitende Demyelinisierung der Nervenbahnen zusammen mit einer Schädigung der Axone des zentralen Nervensystems. Durch die Demyelinisierung der Nervenbahnen kommt es im Krankheitsverlauf zu Gefuehlsstoerungen in den Extremitäten wie Kribbeln, aber auch zu Spastiken und Lähmungserscheinungen. Die molekularen Grundlagen, die an der Entstehung von Multiple Sklerose beteiligt sind, sind sehr vielfältig und bis jetzt noch nicht abschließend erforscht. Diese Doktorarbeit beschäftigt sich mit der Pathophysiologie von Multiple Sklerose und versucht mit Hilfe der Proteomanalyse Rückschlüsse über die Veränderung von Signalkaskaden aufzudecken, die in Zusammenhang mit der Erkrankung stehen. Dazu werden sowohl Liquor und Nervengewebe von Patienten und gesunden Kontroll-Probanden untersucht, als auch verschiedene Stadien der Erkrankung im Tiermodell (Experimentelle Autoimmune Enzephalopathie) simuliert und verglichen.